The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent the work is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
In the standardization of evolved 3rd Generation Partnership Project (3GPPTM) networks, 3GPPTM system architecture evolution (SAE) work is defining a new architecture where both evolved 3GPPTM wireless access (LTE—Long Term Evolution access) and non-3GPPTM accesses are considered. The technical specification (TS) 23.401 “3GPPTM GPRS enhancements for LTE access” [1] and the TS 23.402 “3GPPTM Architecture enhancements for non-3GPPTM accesses” [2], which are incorporated herein by reference in their entirety, contain the current definitions for the architecture and related mechanisms. Specifically, [1] covers one possible implementation of the SAE network that supports LTE accesses, and [2] describes an alternative implementation of the SAE network that supports both LTE and non-3GPPTM accesses.
In a long-term evolution radio access network (LTE RAN), user data packets are transmitted and received between user equipment (UE) and base stations (such as evolved Node-B stations). The user data packets are transmitted and received using protocol stacks that are associated with the UE and the base stations. The protocol stacks each include three service and function layers L1, L2 and L3. The first layer is the bottom most layer and the third layer is the upper most layer. The L1 layer includes a physical layer (PHY). The L2 layer includes a medium access layer (MAC), a radio link control layer (RLC), and a packet data convergence layer (PDCP). The L3 layer includes an Internet protocol layer (IP).
During, for example, an uplink from the UE to a first base station BS1, user data packets are transmitted from the UE to the first base station BS1. When the first base station BS1 successfully receives the user data packets, the first base station BS1 transmits an acknowledgement signal (ACK) to the UE indicating a successful transmission.
Under certain conditions, the UE may not receive the acknowledgement (ACK) signal and may time out. This may result in the user data packets being discarded by the transmitter of the UE. In a LTE RAN, and with respect to a real-time application, the transmitter of the UE sets a timer in association with each of the user data packets. Examples of real-time applications are voice over Internet phone (VoIP) or streaming. When the UE does not receive an ACK signal within a predetermined period after transmission of a corresponding user data packet, the UE times out and discards the user data packet.
During a handover between the first base station BS1 of a first radio access network (RAN) and a second base station BS2 of a target RAN, radio communication between the UE and the first base station BS1 may deteriorate. When a UE is near the outer boundary of the first RAN, radio transmission degrades. As a result of the handover and deteriorated radio communication, the UE may not receive an ACK signal with regard to certain transmitted packets. Thus, the UE may retransmit the packets to the second base station BS2 regardless of whether the first base station BS1 successfully received the packets.